PROJECT SUMMARY Aggression linked to peer-based rejection and bullying is a leading cause of injury and psychological distress among middle school-aged adolescents, and occurs at higher rates in youth exposed to harsh parenting. Tradi- tional intervention programs that target those at risk for perpetrating aggression due to harsh parenting have had only limited success. This lack of success may be due to the fact that aggression is the product of complex decision-making processes that are influenced by current states of attention, arousal, and affect. A different approach is to prevent aggression before it happens by interceding when nonverbal indices signal a shift in these critical states. An essential first step towards establishing this prevention-based approach is to isolate nonverbal behavior that reliably predicts forthcoming aggression in high-risk adolescents. Eye gaze, pupillary dilation, and facial expressions are strong nonverbal behavioral candidates given that they are well-established indices of attention, arousal, and affective states. The current proposal uses computational modeling to test the predictive link between these nonverbal behaviors elicited during an ecologically valid social rejection paradigm and subsequent expression of peer-based aggression in adolescents (11-14 years; N=80) with high and low exposure to harsh parenting. Results will lay the groundwork for our long-term objective, to develop next gen- eration interventions aimed at preventing aggression the moment its behavioral precursors are detected.